Pentaerythritol is conventionally manufactured by the reaction of formaldehyde with acetaldehyde in the presence of an alkali metal hydroxide condensation catalyst, such as sodium hydroxide or potassium hydroxide. In addition to pentaerythritol; dipentaerythritol, tripentaerythritol, other polyhydroxy compounds (usually called organic syrups), and an alkali metal formate are also often produced. Through a rather complex series of concentrations and crystallizations, most of the products of the reaction are separated and recovered. Generally, however, a significant portion of the solid products cannot be further resolved by fractional crystallizations. The concentrated aqueous solution of such residual products is usually referred to herein as pentaerythritol waste liquor.
The conversion of the waste liquor to usable products is desirable because a substantial amount of pentaerythritol or pentaerythritol-like compounds are lost in the waste liquor, and also because the disposal of the waste liquor in an environmentally acceptable manner is costly.
The primary reason that the waste liquor from an alkali metal hydroxide catalyzed PE process is not a useful product is that it contains large quantities (i.e. from about 10% to 30% by wt.) of salts, principally alkali metal formate (usually referred to as ash). If the ash content is reduced to a low level, e.g. about 2% by wt., the mixture of polyhydroxy compounds of the waste liquor can be economically converted to a useful component of commercial resins, e.g. foundry core oils.
Various methods have been proposed for resolving the components of pentaerythritol waste liquors. The most common proposals have involved the extraction of the organic components out of a waste liquor or dried waste liquor with organic solvents such as aliphatic alcohols and tributylphosphate. Other methods proposed have been to remove the inorganic salt by passing the waste liquor through an ion exchange resin, and to remove the organic syrups with a bed of beads of a porous organic polymer.